The present invention relates to a method for repairing leaking or otherwise defective pipelines and more particularly to an improved method for lining steel pipelines with fiberglass pipe.
The facilities required for production of crude oil and related liquids include numerous pipelines. These range from small gathering lines running to and from individual wells to large cross-country pipelines used to transport the liquids over great distances. These pipelines represent a large part of the investment required to produce crude oil especially in remote areas such as northern Alaska. The useful life of these pipelines is generally limited by corrosion which eventually causes the pipelines to leak and/or to lose the strength required in high pressure service.
Numerous repair methods have been used to keep leaking or otherwise defective pipelines in service. The most obvious is to patch or simply replace defective sections of pipeline. Where pipelines are buried, such repair methods are difficult or at least very expensive. Where internal corrosion is the primary problem, various efforts to apply corrosion-resistant coatings, such as epoxy paint, on the internal surface have been attempted with varying degrees of success.
A more effective method has been to insert fiberglass pipe inside defective steel pipelines. Lengths of fiberglass pipe have been joined by conventional bell and spigot joints to form long lengths up to 1,000 feet or more. Other external joint methods such as the butt and wrap method, i.e., a wrap of fiberglass cloth and adhesive, have also been used. Fiberglass pipe has been found to have good strength qualities while being flexible enough to be pulled into existing pipelines, even around corners or curves. This repair method has included injection of cement grout, typically made from common portland cement, into the annular space between fiberglass pipe and steel pipeline. This repair method has been used commercially by Unisert Systems, Inc. of Houston, Texas, and is described in more detail in a paper entitled "Plastic Liners for Pipeline Rejuvenation", March 1984, by Benant E. Fruck of that company.
While this fiberglass pipe lining repair method has considerable advantages as compared with other known repair methods, it has certain disadvantages. Use of any pipe lining system necessarily reduces the inner diameter of the pipeline, thereby reducing its flow capacity. The wall thickness of fiberglass liners have therefore been kept to a minimum. However, use of external collars or any other external joint to connect sections of fiberglass pipe also effectively reduces the final pipeline inner diameter since the effective overall diameter at the joints must be small enough to allow the liner to be pulled into the existing steel pipeline. The use of common cement grout also requires that the maximum outer diameter of the liner be small enough to provide a sufficiently large annular space to allow pumping of the cement grout over long distances, 1,000 feet or more. While common cement grout has very good compressive strength, it has very little tensile strength and does not inherently bond to either the fiberglass liner or the steel pipeline. The cement grout does not inherently form a fluid-tight seal. It greatly increases the weight of the pipeline, which may be an advantage in subsea installations, but is a distinct disadvantage in other situations such as above-ground installations where the support systems may not have sufficient strength.